diff --git a/pallets/collator-selection/src/lib.rs b/pallets/collator-selection/src/lib.rs
index efcb97ddc..ead4a768a 100644
--- a/pallets/collator-selection/src/lib.rs
+++ b/pallets/collator-selection/src/lib.rs
@@ -81,6 +81,7 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 pub use pallet::*;
+pub mod migrations;
 
 #[cfg(test)]
 mod mock;
diff --git a/pallets/collator-selection/src/migrations.rs b/pallets/collator-selection/src/migrations.rs
new file mode 100644
index 000000000..ad341f963
--- /dev/null
+++ b/pallets/collator-selection/src/migrations.rs
@@ -0,0 +1,96 @@
+// This file is part of Astar.
+
+// Copyright (C) Stake Technologies Pte.Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Astar is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Astar is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Astar. If not, see <http://www.gnu.org/licenses/>.
+
+use super::*;
+use frame_support::{pallet_prelude::*, traits::OnRuntimeUpgrade};
+use sp_std::{marker::PhantomData, vec::Vec};
+
+/// One-time migration that removes outdated LastAuthoredBlock entries.
+/// It keeps entries only for accounts that are currently:
+///   - active candidates
+///   - invulnerables
+///
+/// All other accounts are removed.
+pub struct LastAuthoredBlockCleanup<T: Config>(PhantomData<T>);
+
+impl<T: Config> OnRuntimeUpgrade for LastAuthoredBlockCleanup<T> {
+    fn on_runtime_upgrade() -> Weight {
+        log::info!("Running CollatorSelection::LastAuthoredBlockCleanup...");
+
+        // Snapshot active identifiers for faster membership checks
+        let invulnerables = Invulnerables::<T>::get();
+        let candidates: sp_std::collections::btree_set::BTreeSet<T::AccountId> =
+            Candidates::<T>::get().into_iter().map(|c| c.who).collect();
+
+        let mut read = 0u64;
+        let mut write = 0u64;
+        let mut stale = Vec::new();
+
+        // Sanity limit
+        const MAX_SCAN: u64 = 200;
+
+        for (account, _) in LastAuthoredBlock::<T>::iter() {
+            if read >= MAX_SCAN {
+                log::warn!("LastAuthoredBlockCleanup: scan limit {} reached.", MAX_SCAN);
+                break;
+            }
+            read += 1;
+
+            let keep = invulnerables.contains(&account) || candidates.contains(&account);
+            if !keep {
+                stale.push(account);
+            }
+        }
+
+        for account in stale {
+            LastAuthoredBlock::<T>::remove(account);
+            write += 1;
+        }
+
+        log::info!(
+            "LastAuthoredBlockCleanup completed: removed {} entries (reads {}, writes {}).",
+            write,
+            read,
+            write
+        );
+
+        <T as frame_system::Config>::DbWeight::get().reads_writes(read, write)
+    }
+
+    #[cfg(feature = "try-runtime")]
+    fn pre_upgrade() -> Result<Vec<u8>, sp_runtime::TryRuntimeError> {
+        let old_count = LastAuthoredBlock::<T>::iter().count() as u64;
+        Ok(old_count.encode())
+    }
+
+    #[cfg(feature = "try-runtime")]
+    fn post_upgrade(data: Vec<u8>) -> Result<(), sp_runtime::TryRuntimeError> {
+        let old_count: u64 = Decode::decode(&mut &data[..]).map_err(|_| {
+            sp_runtime::TryRuntimeError::Other("Failed to decode pre-upgrade count")
+        })?;
+
+        let new_count = LastAuthoredBlock::<T>::iter().count() as u64;
+
+        assert!(
+            new_count < old_count,
+            "LastAuthoredBlockCleanup: new count > old count (should only decrease)"
+        );
+
+        Ok(())
+    }
+}